Offset edges along a plane
I'm using 2.76 And it all works just fine. Here are the steps:
You need to install the addon

Download the Add-on from the link in this page: https://github.com/Bombaba/BlenderPythonScripts/blob/master/mesh_offset_edges.py



To install the Add-on in Blender:
Press Ctrl Alt U to open the User Preferences window. Go to the Add-ons Tab and press on Install from File:



Select the file you had downloaded earlier and click on istall from file

Back on the User preferences window find the Mesh section and enable Mesh:Offset Edges by clicking on the box on the right.
To make the add-on permanent on your blender installation press the Save User Settings button.

The add-on is now available and ready for use.

Select the object you want to work on and enter edit mode (Tab)

Select the edges you want to affect and press Ctrl E. The offset Edges option should be available in the Edges Menu.




The options for the tool will be displayed on the Toolshelf (T) or by pressing F^